In the rolling of aluminum and aluminum alloy sheet material, it is customary to flood the rolls and sheet material with a coolant for the purpose of reducing friction and carrying away heat generated by the operation. The coolant generally comprises a mineral oil-in-water emulsion and various non-petroleum additives. Numerous compositions having satisfactory coolant and friction-modifying properties are known in the prior art.
One disadvantage of prior art mineral oil/water emulsion coolants is that they are degraded at elevated temperatures especially the high temperatures employed in hot rolling of metals. Upon degradation, soaps are formed which cause smudging of the metal sheet. Such degradation is accelerated at high temperatures by evaporation of low molecular weight components of the oil and by oxidation. Because of these changes, there is an increase in sludge formation and an increase in lubricant viscosity. The ultimate result may be loss of mill control.
In order to deal with the above-listed effects in a hot rolling environment, one or more countermeasures is customarily employed. Oxidation inhibitors are added to the coolant; the used coolant is filtered and distilled to recover useful components; and, as a last resort, the used coolant is completely discarded. Because each of these countermeasures involves additional expense, there are several benefits to be gained if a hot rolling lubricant is formulated to have increased resistance to degradation.
A principal objective of the present invention is to provide a lubricant composition having increased resistance to degradation at elevated temperatures
A related objective of the invention is to provide an oil-free lubricant composition having satisfactory friction and wear characteristics for hot rolling aluminum alloy sheet material.
It is a further object of the present invention to provide a metalworking method using the claimed lubricant composition.
Additional objects and advantages of the present invention will become apparent to persons skilled in the art from the following detailed description.